Platelet factor 4 (PF4) is a well-known protein which has been completely sequenced (Deuel et al. Proc. Natl. Acad. Sci. USA 78:4585, 1981). It is a 70-residue secretable platelet protein with a molecular weight of approximately 7.8 Kd which is released during platelet aggregation.
PF4 possesses characteristic structural features of the pro-inflammatory proteins interleukin-8 and .beta.-thromboglobulin.
PF4 has been reported to inhibit the growth of melanoma and colon carcinoma in vivo, but not in vitro (Sharpe et al. (1990) J. Natl. Cancer Inst. 82:848-853; Maione et al. (1991) Cancer Res. 51:2077-2083).
It has been suggested that PF4 may inhibit growth of Kaposi sarcoma cells in vitro (Zucker et al. (1991) Proc. Soc. Exp. Biol. Med. 198:693-702; Miles et al. (1991) [abstract] VII International Conference on Aids (1991) Florence, Italy).
Hiti-Harper et al. (Science 199:99, 1978) report that PF4 inhibits collagenase derived from cultured human skin or human granulocytes.
Horton et al. (Biochim. Biophys. Acta 630:459, 1980) report that PF4 inhibits parathyroid hormone-stimulated .sup.45 Ca release from fetal rat bone in vitro.